I have a circuit that goes to a lot of stuff and it was tripping a 20a breaker but it was only once every few days, up to a week. The circuit was lightly used and cruised at less than an amp at the breaker until some outside lights came on, then it was still less than 2 amps. I swapped breakers right away since I had the panel open to look at the current. I kept taking things away until I had it isolated to one motion detector. The GFCI this was on sometime tripped but not always. (usually not) I still don't believe it but replacing the M/D seemed to fix it. It has been several days with no problem. After a couple days I decided the M/D was bad and I broke into it. I didn't see anything burnt or any other thing out of whack. I had that box open a few times in this process and there was nothing unusual going on. I couldn't make it fail moving the wires around hot and I didn't see anywhere that showed a burnt spot. I really expected a fault that tripped a 20 would leave a mark. This is an all plastic M/D without a green wire but all indications pointed to a line to ground fault. In a race, the GFCI should win every time. The test button does work and this is the new style "smart" one. I suppose I should just move on but I am curious. Have you seen anything like this.

I have not seen it but wonder if a semiconductor was short circuiting through its innards, thus not visible. A line to neutral fault, very low impedance, and it has the possibility of not hurting the case of the semiconductor.

Shane